Where the salmon roam: fjord habitat use of adult Atlantic salmon

The habitat use of adult Atlantic salmon was evaluated in a fjord complex in western Norway. A representative sample of 9 wild and 29 hatchery origin Atlantic salmon were tagged with acoustic tags and tracked with 28 stationary receivers from June 2012 to river entry. Using a movement-based kernel density estimation, we identified near shore habitat use in relation to a National Salmon Fjord (NSF) and adjoining aquaculture sites. Furthermore, we compared progression rates and vertical distributions among habitat units. Mean residence time for salmon with acoustic tags from marking to river entry was 30 days (range 3-83 days). Moreover, recaptures of individuals with T-bar anchor tags supported the long residency of Atlantic salmon within the fjord (0-63 days). The main habitat use occurred outside the NSF (68%), with 62% of the individuals overlapping with one or more aquaculture sites. Median progression rates ranged from 15 km d(-1) up to 42 km d(-1) among the different sections of the fjord with a mean vertical distribution <2m from the surface. Whereas direct implications from the overlap with aquaculture are unclear, the results illustrate the challenge encountered when evaluating the effectiveness of marine protected areas in close proximity to aquaculture sites.